The use of Active Noise Reduction (ANR) headphones, which isolates the user from the ambient sound (for instance car/aircraft engine noise, fan noise, train/metro) by means of anti-sound played through the headphone loudspeakers is growing. In conventional headphones, the anti-sound is calculated from microphones placed on the headphone.
There exist a wide variety of active noise reduction (ANR) systems for headsets. Conventional feed forward active noise reduction systems pick up a “reference noise” signal, and play a filtered version of this reference signal such that it reduces the noise perceived by the user of the headset. The filtering can be performed in the analog domain, of in the digital domain. Due to the fact that the reference noise is registered using a microphone, the filtering is performed on all the ambient noise and the consequent reduction is non-selective.